CN112262523A

CN112262523A - Isolated active EMI filter without additional element on power line

Info

Publication number: CN112262523A
Application number: CN201980029888.2A
Authority: CN
Inventors: 金嗔国; 郑想永; 申东一
Original assignee: UNIST Academy Industry Research Corp
Current assignee: UNIST Academy Industry Research Corp
Priority date: 2018-05-02
Filing date: 2019-05-02
Publication date: 2021-01-22
Also published as: JP2022174125A; JP2024084850A; US12095433B2; JP2021524182A; DE112019002248T5; JP7475720B2; WO2019212258A1; JP7141623B2; US20210058070A1; KR101945463B1

Abstract

The present invention discloses an EMI filter for preventing noise emitted through a power line cable, an isolated type active EMI filter without an additional component on the power line comprising: a common mode choke coil disposed on the power supply side; a Y capacitor disposed on the EMI source side; a sense winding to sense current; an amplifying unit that amplifies the noise current; and injecting the signal of the secondary coil as a compensation signal into a transformer of the Y capacitor.

Description

Isolated active EMI filter without additional element on power line

Technical Field

The present invention relates to an EMI filter, and more particularly, to an isolated active EMI filter without an additional component on a power line.

Background

In most home/industrial electrical systems, EMI filters are installed to prevent conducted EMI noise emitted through the power line cables.

In order to prevent the common mode conducted noise, a filter composed of a common mode choke coil and a Y capacitor is generally used. In a high power/high current electrical system, the self-saturation of the common mode choke reduces the noise reduction performance, and to prevent this, a multistage filter or an expensive high performance choke must be used to obtain sufficient attenuation performance, which results in a significant increase in the size and price of the filter. Therefore, attempts have been made to use an active EMI filter that can overcome the limitations of a passive EMI filter and effectively improve performance, and preferably without a choke coil added to a power supply line due to the active EMI filter.

The active EMI filter has a feedback circuit structure that can sense a noise voltage or current through a capacitor or transformer and apply a compensation voltage or current back to the transformer or capacitor to cancel it out. However, if the active EMI filter senses and compensates for noise by adding a transformer to the power line, the performance of the high power/high current electrical system will be greatly reduced due to self-saturation of the transformer. That is, in the related art, an active EMI filter without adding a transformer on a power line, noise sensing and noise compensation are performed by a capacitor.

However, when the active EMI filter connects the capacitor to the power line to sense and compensate for noise, the active circuit element is not isolated from the power line, and thus reliability and stability against Electrical Overload (EOS) are greatly reduced. In other words, there is a need for a structure that does not add a choke coil to a power supply line due to an active EMI filter, and can isolate active circuit elements from the power supply line.

Disclosure of Invention

Technical subject

An object of the present invention is to provide an isolated active EMI filter having no additional element on a power line, in which an active circuit element is isolated from the power line even if there is no additional element on the power line.

Another problem to be solved by the present invention is to provide a method of reducing EMI noise by using an isolated type active EMI filter having no additional element on a power line, which isolates an active circuit element from the power line even if there is no additional element on the power line.

Technical solution

To achieve the object, an isolated active EMI filter without an additional element on a power line according to embodiment 1 of the present invention includes: a Common Mode (CM) Choke coil (hook) disposed on a power supply side of a power supply, and having a winding wound around a Live line (Live line) and a Neutral line (Neutral line) connected to an EMI source, respectively; a Y capacitor, which is disposed at one side of an EMI source generating EMI, and is composed of two capacitors connected in series, the two capacitors being connected in parallel between the line and neutral lines and connected in common with a ground; a sensing winding which is rewound on the common mode choke coil through a coil and senses a noise current of the common mode choke coil; an amplifying unit that amplifies a noise current sensed by the sensing winding; and a transformer provided at a front end of the Y capacitor, a primary coil receiving the amplified signal from the amplifying unit, a secondary coil connected to a ground connected to the Y capacitor so as to be isolated from a power supply line (isolated), and injecting a signal of the secondary coil as a compensation signal into the Y capacitor.

To achieve the object, an isolated active EMI filter without an additional component on a power line according to embodiment 2 of the present invention includes: a Common Mode (CM) choke coil disposed on a power supply side of a power supply and having a winding wound around a Live line (Live line) and a Neutral line (Neutral line) connected to an EMI source, respectively; a Y capacitor, which is disposed at one side of an EMI source generating EMI, and is composed of two capacitors connected in series, the two capacitors being connected in parallel between the line and neutral lines and connected in common with a ground; a transforming unit installed at a front end of the Y capacitor, a primary coil sensing a noise voltage of the Y capacitor, a secondary coil transforming the noise voltage and isolating (isolated) the noise voltage from a power line; an amplifying unit that amplifies the noise voltage sensed by the transforming unit and transformed; a compensation winding that is rewound on the common mode choke coil through a coil and injects the noise signal amplified by the amplification unit into the common mode choke coil.

To achieve the object, an isolated active EMI filter without an additional element on a power line according to embodiment 3 of the present invention includes: a Common Mode (CM) choke coil disposed on an EMI source side that generates EMI, and having a winding wound around a Live line (Live line) and a Neutral line (Neutral line) connected to the EMI source, respectively; a Y capacitor, which is configured on the power supply side of the power supply and consists of two capacitors connected in series, wherein the two capacitors are connected in parallel between the live line and the neutral line and are commonly connected with the ground; a sensing winding which is rewound on the common mode choke coil through a coil and senses a noise current of the common mode choke coil; an amplifying unit that amplifies a noise current sensed by the sensing winding; and a transformer provided at a front end of the Y capacitor, a primary coil receiving the amplified signal from the amplifying unit, a secondary coil connected to a ground connected to the Y capacitor so as to be isolated from a power line (isolated), and injecting a signal transformed by the secondary coil as a compensation signal into the Y capacitor.

To achieve the object, an isolated active EMI filter without an additional element on a power line according to embodiment 4 of the present invention includes: a Common Mode (CM) choke coil disposed at one side of an EMI source generating EMI, and having a winding wound around a Live line (Live line) and a Neutral line (Neutral line) connected to the EMI source, respectively; a Y capacitor, which is configured on the power supply side of the power supply and consists of two capacitors connected in series, wherein the two capacitors are connected in parallel between the live line and the neutral line and are commonly connected with the ground; a transformer disposed at a front end of the Y capacitor, a primary coil sensing a noise voltage from the Y capacitor and transforming it through a secondary coil, and being isolated from a power line (isolated); an amplifying unit that amplifies the noise voltage transformed by the transformer; a compensation winding that is rewound on the common mode choke coil through a coil and injects the noise signal amplified by the amplifying unit into the common mode choke coil as a compensation signal.

To achieve the other objects, a method of reducing EMI noise by using an isolated type active EMI filter without an additional element on a power line according to embodiment 1 of the present invention as a method of reducing EMI noise by adding an active element on a passive EMI filter including a Common Mode (CM) choke coil disposed on a power supply side of a power supply and a Live line (Live line) and a Neutral line (Neutral line) connected to an EMI source are respectively wound with windings; and a Y capacitor, disposed on one side of an EMI source generating EMI, composed of two capacitors connected in series, the two capacitors being connected in parallel between the line and neutral and commonly connected to ground, characterized in that: the method comprises the following steps: a step of sensing a noise current of the common mode choke coil through a sensing winding formed by rewinding a coil on the common mode choke coil; amplifying the noise current induced by the induction winding; and transforming the amplified signal received through a primary coil of a transformer installed at a front end of the Y capacitor through a secondary coil and injecting it into the Y capacitor, wherein the secondary coil of the transformer is connected to a ground connected to the Y capacitor, thereby being isolated from a power supply line (isolated).

To achieve the other objects, a method of reducing EMI noise by using an isolated type active EMI filter without an additional element on a power line according to embodiment 2 of the present invention as a method of reducing EMI noise by adding an active element on a passive EMI filter including a Common Mode (CM) choke coil disposed on a power supply side of a power supply and a Live line (Live line) and a Neutral line (Neutral line) connected to an EMI source are respectively wound with windings; and a Y capacitor, disposed on one side of an EMI source generating EMI, composed of two capacitors connected in series, the two capacitors being connected in parallel between the line and neutral and commonly connected to ground, characterized in that: the method comprises the following steps: a step of sensing a noise voltage using the Y capacitor as a sensing capacitor by a primary coil of a transformer installed at a front end of the Y capacitor and transforming a voltage by a secondary coil of the transformer; a step of amplifying the noise voltage transformed by the secondary coil; and injecting the amplified noise signal into the common mode choke through a compensation winding formed by rewinding the common mode choke with a coil, wherein a secondary coil of the transformer is connected to a ground connected to the Y capacitor so as to be isolated from a power supply line (isolated).

To achieve the other objects, a method of reducing EMI noise by using an isolated type active EMI filter without an additional element on a power line according to embodiment 3 of the present invention as a method of reducing EMI noise by adding an active element on a passive EMI filter including a Common Mode (CM) choke coil disposed at one side of an EMI source generating EMI, and a Live line (Live line) and a Neutral line (Neutral line) connected to the EMI source are respectively wound with windings; and a Y capacitor, which is disposed on a power supply side of a power supply and is composed of two capacitors connected in series, the two capacitors being connected in parallel between the live line and the neutral line and connected in common to a ground, characterized in that: the method comprises the following steps: a step of sensing a noise current of the common mode choke coil through a sensing winding formed by rewinding the common mode choke coil with a coil; amplifying the noise current sensed by the sensing winding; and transforming the amplified signal inputted through a primary coil of a transformer installed at a front end of the Y capacitor through a secondary coil and injecting it into the Y capacitor as a compensation signal, wherein the secondary coil of the transformer is connected to a ground connected to the Y capacitor, thereby being isolated from a power line (isolated).

To achieve the other objects, a method of reducing EMI noise by using an isolated type active EMI filter without an additional element on a power line according to embodiment 4 of the present invention as a method of reducing EMI noise by adding an active element on a passive EMI filter including a Common Mode (CM) choke coil disposed at one side of an EMI source generating EMI, and a Live line (Live line) and a Neutral line (Neutral line) connected to the EMI source are respectively wound with windings; and a Y capacitor, which is disposed on a power supply side of a power supply and is composed of two capacitors connected in series, the two capacitors being connected in parallel between the live line and the neutral line and connected in common to a ground, characterized in that: the method comprises the following steps: sensing a noise voltage of the Y capacitor through a primary coil of a transformer installed at a front end of the Y capacitor, and converting the voltage through a secondary coil; amplifying the transformed noise voltage; and a step of injecting the amplified noise signal as a compensation signal into the common mode choke coil through a compensation winding formed by rewinding the common mode choke coil with a coil, wherein a secondary coil of the transformer is connected to a ground connected to the Y capacitor so as to be isolated from a power supply line (isolated).

ADVANTAGEOUS EFFECTS OF INVENTION

In most electric and electronic appliances for home/industrial use, an EMI filter must be installed to prevent conducted EMI noise emitted through a power line cable, but the isolated active EMI filter without additional components on the power line and the method of reducing EMI noise using the same according to the present invention can obtain the same noise reduction performance in a smaller size and at a lower cost than the case of using only a passive filter.

In addition, according to the present invention, when a conventional multistage passive EMI filter is used to sufficiently reduce noise, the number of stages of the filter can be reduced and the size and cost of most electrical and electronic devices can be reduced by adding an isolated active EMI filter according to the present invention without an additional element on a power supply line.

Drawings

Fig. 1 is a circuit diagram showing the configuration of embodiment 1 of the isolated active EMI filter without additional components on the power line according to the present invention.

Fig. 2 shows a configuration of a proposed transformer isolation AEF additionally ((add-on)) mounted to a CM L-C EMI filter, according to an example of the configuration of the AEF of the present invention.

FIG. 3 shows a circuit model of an AEF according to an embodiment of the invention.

Fig. 4 shows an equivalent circuit including half of the parasitic component (half portion).

Fig. 5 shows a CM choke equivalent circuit model in the power supply line including the influence of the sensing winding.

FIGS. 6a, 6b and 6C show the capacitive effect (C) of the current path and Y capacitance of the active EMI filter in each frequency domain_Y，_eff(s)) of a plurality of cells.

FIG. 7 shows the power line impedance (Z) as viewed in the power direction from the Y capacitor position_line) Curve line. (a) Show N_sen(b) shows N in case of violating equation 19_senThe case when equation 19 is satisfied.

FIG. 8 is a comparison of the loop gain, where (a) shows the gain in the absence of the damping component R_d1、C_d、R_d2And a phase compensator R_c、C_cThe loop gain in the unstable case of (a), (b) shows the loop gain in the stable case of the presence of these components.

Fig. 9 is a circuit diagram of embodiment 2 of the isolated active EMI filter without additional components on the power line according to the present invention.

Fig. 10 is a circuit diagram of embodiment 3 of an isolated active EMI filter without additional components on the power line in accordance with the present invention.

Fig. 11 is a circuit diagram of embodiment 4 of the isolated active EMI filter without additional components on the power line according to the present invention.

Fig. 12 shows a flowchart of a method for reducing EMI noise by adding an active component in a passive EMI filter, which corresponds to embodiment 1 of the isolated active EMI filter without an additional component on the power line according to the present invention.

Fig. 13 shows a flowchart of a method for reducing EMI noise by adding an active component in a passive EMI filter, which corresponds to embodiment 2 of the isolated active EMI filter without an additional component on the power line according to the present invention.

Fig. 14 shows a flowchart of a method for reducing EMI noise by adding an active component to a passive EMI filter, which corresponds to embodiment 3 of the isolated active EMI filter without an additional component on the power line according to the present invention.

Fig. 15 shows a flowchart of a method for reducing EMI noise by adding an active component in a passive EMI filter, which corresponds to embodiment 4 of the isolated active EMI filter without an additional component on the power line according to the present invention.

Detailed description of the preferred embodiments

The present invention relates to an isolated active EMI filter without an additional component on a power line and a method for reducing EMI noise using the isolated active EMI filter, wherein the isolated active EMI filter includes a power supply side Common Mode (CM) choke coil configured to supply power; a Y capacitor; a sensing winding which is rewound on the common mode choke coil through a coil and senses a noise current of the common mode choke coil; an amplifying unit amplifying a noise current sensed by the sensing winding; and a transformer provided at a front end of the Y capacitor, a primary coil receiving the amplified signal from the amplifying unit, a secondary coil connected to a ground connected to the Y capacitor so as to be isolated from a power line (isolated), and injecting a signal of the secondary coil as a compensation signal into the Y capacitor.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Since the embodiments described in the present specification and the configurations shown in the drawings are only preferred embodiments of the present invention and do not represent all the technical spirit of the present invention, it should be understood that embodiments may be substituted for their various equivalents and modifications for the present application.

Fig. 1 shows a configuration circuit diagram of a 1 st embodiment of an isolated active EMI filter without additional components on a power line according to the present invention. The 1 st embodiment of the present invention includes a passive EMI filter consisting of a Common Mode (CM) choke 110 and a Y capacitor 120, and an EMI filter 100 consisting of a sensing winding 130, an amplifying unit 140, and a transformer 150.

A Common Mode (CM) choke 110 is provided on the power supply side of the power supply, and a Live line (Live line) and a Neutral line (Neutral line) connected to an EMI source are wound with windings, respectively.

The Y capacitor 120 is disposed at one side of the EMI source generating EMI, and is composed of two capacitors connected in series, which are connected in parallel between the line (L) and neutral (N) and are commonly connected to ground.

The sensing winding 130 is rewound on the common mode choke 110 by a coil, and senses a noise current flowing in the common mode choke 110. When the capacitance of the parasitic circuit of the common mode choke coil 110 is C cm, the capacitance of the parasitic circuit of the sensing winding 130 is C sen, and the number of turns (N sen) of the sensing winding 130 is preferably less than the square root of 2C cm/C sen.

The amplifying unit 140 amplifies the noise current sensed by the sensing winding 130.

The transformer 150 is provided at the front end of the Y capacitor 120, a primary coil receives the amplified signal from the amplifying unit, a secondary coil is connected to the ground connected to the Y capacitor 120 so as to be isolated from the power line (isolated), and the signal of the secondary coil is injected into the Y capacitor 120 as a compensation signal.

Fig. 2 shows a configuration of a proposed transformer isolation AEF additionally ((add-on)) mounted to a CM L-C EMI filter, according to an example of the configuration of the AEF of the present invention. FIG. 3 shows a circuit model of an AEF according to an embodiment of the invention.

According to the present invention, the isolated type active EMI filter without additional components on the power line may further include a low voltageA Low pass filter (Low pass filter) to prevent stability problems due to winding resonance in the high frequency range (see fig. 3). The low-pass filter comprises a resistor (R)_f) And a capacitor (C)_f)。

Resistance (R)_f) Is connected to the sense winding and the other end is connected to the + input terminal of the amplifying unit. The capacitor (C)_f) Is connected to the resistor (R)_f) And a + input terminal of the amplifying unit, the other end being connected to ground and located at an input end of the amplifying unit.

In addition, it is preferable that the impedance (Z) from the input terminal of the amplifying unit 140 toward the low-pass filter is in the frequency range of interest_in，AEF) Is set higher than the parasitic RC component impedance (Z) of the sensing winding 130_sen，para)。

Preferably, the cut-off frequency (1/2 ^ R) of the low-pass filter_fC_f) Greater than the maximum operating frequency (f)_op,max) And is less than frequency

(k_senIs the coupling coefficient of the sense winding 130; n is a radical of_senIs the number of turns of the sense winding 130; l is_cmIs the inductance of common mode choke 110; c_senIs the capacitance of the parasitic circuit of the sense winding 130).

In addition, the isolated active EMI filter without additional components in the power line according to the present invention may further include a bypass branch having stability as a bypass and damping circuit to avoid resonance in the transformer and mitigate performance degradation due to resonance between EMI source impedance and the Y capacitor. (refer to fig. 3). The Bypass branch (Bypass branch) may comprise a 1 st resistor (R)_d1) And a capacitor (C)_d) And the 2 nd resistance (R)_d2)。

1 st resistance R_d1One terminal of which is connected to the Y capacitor and the other terminal of which is connected to the secondary winding of the transformer, a capacitor C_dIs connected to one end of the resistor. Resistance R of No. 2_d2Is connected in series with the other end of the capacitor, the other end being connected to ground.

In addition, the isolated type active EMI filter without an additional element in the power line according to the present invention may further include a phase compensator for maintaining stability in a low frequency range (refer to fig. 3).

The phase compensator includes a resistor (Rc) and a capacitor (Cc) connected in parallel, and one end of the resistor (Rc) and the capacitor (Cc) connected in parallel is connected to a (-) input terminal of the amplifying unit, and the other end of the resistor (Rc) and the capacitor (Cc) connected in parallel is connected to an output terminal of the amplifying unit.

The invention provides a new structure of a complete (full) transformer isolation AEF. Referring to fig. 2, an AEF according to an embodiment of the present invention is additionally installed (add-on) to an existing CM L-C EMI filter composed of a CM choke and a Y capacitor. The AEF structure according to one embodiment of the invention is similar to a conventional CSCC AEF topology, but with the addition of an injection (injection) transformer between the output of the amplifying cell and the compensating Y-capacitance. Since the injection transformer is not installed on the main power line, only a small amount of compensation signal current flows through the transformer. The injection transformer can be implemented in small size because its current is small regardless of the applied operating current, thereby reducing the risk of magnetic saturation and thermal problems. In addition, the sensing part of the AEF does not need an additional transformer, but a fine noise sensing line is additionally wound on the existing commercial CM choke coil. Attempts have been made to add sensing winding (sensing winding) directly to commercial CM chokes, but the adverse effects of the sensing winding and the maximum allowed number of turns (turn) have not been investigated. In summary, the main novel feature of the AEF according to one embodiment of the present invention is that the main power supply line is fully transformer-isolated without using a separate component, and a specific compact size design (compact sized design) can be adopted. Due to these characteristics, the AEF according to the invention has a smaller size and better performance compared to CSVC AEF with other transformer isolations.

The present invention provides a number of useful explicit design guidelines for the complete design of an AEF according to one embodiment of the present invention. As described below, transformer isolated AEFs were analyzed to evaluate noise attenuation performance, and based on this, appropriate design guidelines were provided for the performance and stability of the AEF, and the filter insertion loss and loop gain of the AEF were measured and verified by a Vector Network Analyzer (VNA). CM CE noise reduction by AEF can also be seen on the actual product SMPS board. In addition, the leakage current to ground was measured to confirm the safety of AEF use.

Next, AEF according to an embodiment of the present invention will be analyzed. In fig. 3, CY represents the capacitance of the Y capacitance. The CM choke is modeled by Lcm and Mcm and represents the self-inductance and mutual inductance of the windings on the power line.

The AEF consists mainly of a sensing winding (sensing winding) wound on a CM choke, an amplifying unit and an injection transformer. Setting the winding ratio of the winding on the power supply line to the sensing winding to 1: n is a radical of_senThe self-inductance of the sensing winding is about N_sen ²L_cm。M_senRepresenting the mutual inductance between the windings of the power line and the sensing winding of the AEF input. Similarly, M_injRepresents the mutual inductance of the injection transformer, and the ratio of the primary and secondary windings is set to 1: n is a radical of_inj. The self-inductance of each side is L_injAnd N_inj ²L_inj。M_cm、M_senAnd M_injAre respectively represented by k_cmL_cm、k_senN_senL_cmAnd k_injN_injL_injAnd (4) calculating. Here, k is_cm、k_senAnd k_injRepresenting each coupling coefficient. In practical design, k_cm、k_senAnd k_injThe value of (b) is typically in the range of 0.99 to 1. The amplifying unit is configured with a resistor R₁And R₂The non-inverting operational amplifier of (1).

Several additional components are required in view of the feedback stability of the AEF, such as a low pass filter, a bypass branch and a phase compensator, as shown in fig. 3. R_fAnd C_fA low pass filter is formed in the operational amplifier to prevent high frequency range due to the sensing windingStability problems due to resonance. R_d1、C_dAnd R_d2The shunt and damping circuits operate for stability to avoid resonance in the injection transformer, thereby further mitigating performance degradation due to resonance between the noise source impedance and the Y-capacitor. R_cAnd C_cIs a phase compensator which ensures stability in a low frequency range.

Even if the ground reference voltage of AEF is set to be different from the ground, AEF is symmetrical with respect to the AC zero potential, and can be analyzed by dividing the circuit. Fig. 4 shows an equivalent circuit including half of the parasitic component (half portion). Referring to fig. 4, to more accurately show, the parasitic circuit parameters of the CM choke, sense winding and injection transformer were also modeled, respectively containing R_cm、C_cm、R_sen、C_sen、R_inj1、C_inj1、R_inj2And C_inj2. Respectively modeling CM noise sources of tested Equipment (Equipment under Test, EUT) as Thevenin equivalent circuit V_nAnd Z_nTo represent the voltage and impedance of the CM noise source. Z_LISNRepresenting the impedance of the Line Impedance Stabilization Network (LISN). Z_line、Z_line、_AEFAnd Z_Y、_effRespectively representing the impedance in each direction with respect to the ac zero potential.

The operating principle of the AEF was analyzed and the effective inductance of the CM choke was explained according to the expression of the effective inductance of the CM choke and the effective capacitance of the Y capacitive branch.

Using Kirchhoff's law, the impedance from the CM choke front end toward the power supply line is as follows.

[ equation 1]

Wherein,

[ formula 2]

L_cm，eff(s)＝(1+k_cm-X(s))L_cm

[ formula 4]

[ formula 5]

L_cm，effThe effective inductance of the CM choke is represented, where the inductance cancellation term x(s) appears. X(s) is defined as (2M)_senI_sen)/(L_cmI_cm) In which I_cmAnd I_senRespectively, in FIG. 4, through the inductive branch (branch) (L)_cm+M_cm) And 2N_sen ²L_cmThe current of (2). Z_sen，paraRepresenting the parasitic RC component impedance of the sense winding. Z_in，AEFRepresenting the impedance from the input of the amplification unit towards the low-pass filter. Assuming that the input impedance of the operational amplifier is greater than the target frequency range, it is ignored in equation 5.

Fig. 5 shows a CM choke equivalent circuit model in the power supply line including the influence of the sensing winding. Fig. 5 summarizes the effect of the sensing winding on the CM choke inductance. Referring to FIG. 5, the right box shows the box considered by 2M_senCM choke equivalent circuit model in the power supply line for induced voltages. Induced voltage 2sM_senI_senPolarity of (c) and s (L)_cm+M_cm)I_cmThe polarity of the voltage drop of (a) is opposite. If X(s) is defined as (2M)_senI_sen)/(L_cmI_cm) Then the total voltage of the choke inductor can be reduced to s (1+ k)_cm-X(s))L_cmI_cm. Therefore, as shown in equation 2, the effective inductance L of the CM choke_cm，effIs represented by (1+ k)_cm-X(s))L_cm。

If there is no sense of discomfortSide winding, then k_senX(s) is 0, so L_cm，effCan be simply expressed as (1+ k)_cm)L_cm. However, when sN in equation 3_sen ²L_cmIs much higher than (Z)_in,AEF||Z_sen,para) When k is_cmAnd k_senVery close to 1, so X(s) is ≈ 2k_sen ²，L_cm,eff≈L_cm(1+k_cm-2k_sen ²). This means that the current flowing through the sensing winding can have a decisive influence on the choke inductance. Therefore, in order to maintain the choke inductance, the number of turns N of the sensing winding must be limited_sen。

Next, the effective capacitance of the Y capacitance will be explained. Towards Y capacitor branch Z_Y，effCan be expressed by equation 6 to equation 11.

[ formula 6]

Wherein,

[ formula 7]

[ formula 8]

[ formula 9]

[ equation 10]

[ formula 11]

Here, α(s) and β(s) may be physically understood as a boosting factor and a bypassing factor, respectively, as described later. G₁(S) is from V_inTo V_in，ampVoltage gain of (G)_amp(s) is from V_in，ampTo V_out，ampThe gain of the amplifying unit of (1). The frequency bandwidth of the operational amplifier is assumed to be sufficiently higher than the target frequency range. Z in equation 6_Y，effCan be understood as the effective capacitance C_Y，effThe impedance of (S), which is defined as shown in equation 12.

[ formula 12]

FIGS. 6a, 6b and 6C show C as a function of frequency_Y，eff(s), FIG. 6a shows the AEF operation over a frequency range, FIG. 6b shows a plot (plot) of α(s) and β(s), and FIG. 6c shows Z_Y，effImpedance curve of (2).

C as a function of frequency is summarized in FIGS. 6a, 6b and 6C_Y，eff(s) is varied. The effect of AEF on the Y capacitive branch and the change in the current path are shown in fig. 6 a. Dashed box shows AEF vs C_Y，effThe influence of (c). f. of_op，minAnd f_op，maxAre the minimum and maximum target operating frequencies of the AEF, which can be designed by the circuit parameters of the AEF, respectively.

For example, the magnitude of α(s) and β(s) for a properly designed AEF are plotted against the frequency in FIG. 6 b. The impedance Z of the Y capacitive branch is also plotted in FIG. 6c_Y，eff. At a temperature sufficiently lower than f_op，minAt frequencies of (a) and (b) are both much smaller than 1, and Z in equation 6_Y，effIt is simply approximately 1/sCY. This means that the bypass circuit and injection transformer are negligible compared to the impedance of CY and the noise voltage compensated by AEF is very small. At a time from f_op，minTo f_op，maxIn the AEF operating frequency range of (1), α(s) is greater than 1, but β(s) is still much less than 1. That is, the AEF provides a compensation voltage to the Y capacitor branch, e.g., - α V in FIG. 6a_inAs shown, the bypass circuit is still negligible.

The magnitude of α(s) is maintained mainly at the product of the voltage gains of the sensing winding, the amplifying unit and the injection transformer, i.e. N, in the operating frequency range_senN_inj(1+R₂/R₁) The range of (1). Therefore, the CM current flowing through the Y capacitor branch is based on (1+ N)_senN_inj(1+R₂/R₁) Amplification, as shown in FIG. 6c, the effective capacitance increases to (1+ N)_senN_inj(1+R₂/R₁))C_Y. As the frequency increases to approach f_op，maxα(s) starts to decrease, which indicates that the compensation voltage from the AEF decreases. Meanwhile, β(s) is similar to 1, which means the impedance (R) of the bypass branch_d2+1/sC_d) Lower than the impedance of the injection transformer path. Therefore, the CM noise current flows mainly through the bypass branch, Z_Y，effHas an impedance of approximately (1/sC)_Y+2(R_d2+1/sC_d))。

FIG. 6c shows at f_op，maxIn the latter frequency range, because of C_dAnd R_d2Is added to the current path, so Z_Y，effRelative to 1/sC_YThe size of (a) increases more. However, the damping resistance R_d2Plays an important role in mitigating resonance between the Y capacitance and the CM noise source impedance. Since the performance of the entire CM filter is usually greatly reduced by resonance, resonance should be avoided.

Next, the insertion loss of the entire filter will be described. The noise attenuation performance of a filter is typically quantified as the Insertion Loss (IL), which is defined as the ratio of the noise voltage received by the LISN without the filter to the noise voltage of the LISN with the filter installed. In fig. 4, IL for the entire EMI filter is derived as shown in equation 13.

[ formula 13]

The insertion loss IL of equation 13 is mainly in Z with increasing frequency_Y，effBecomes smaller than Z_lineBegins to increase. The low frequency boundary of the filter operation may be approximated as

As shown in FIG. 6c, the proposed AEF greatly reduces Z within the target frequency range_Y，effThis increases the IL of the overall filter. Furthermore, the AEF allows the entire filter to start operating at a lower frequency.

On the other hand, the design guidelines of the AEF provided by the present invention will be described. Practical design guidelines are developed for AEF, taking into account performance and stability. First, the design of the sensing winding and the input low pass filter will be described.

The induction winding is wound directly on the CM choke, so that no additional induction transformer needs to be added. In terms of size and cost, it is preferable not to use a separate sensing transformer. However, as described above, the CM choke inductance L can be reduced by the additional sensing winding_cm，effAnd power line impedance Z_line. Even though the AEF according to the invention improves the Y capacitance C well_Y，effReduced power line impedance Z_lineThe noise attenuation performance of the entire CM EMI filter is also deteriorated. Therefore, to prevent Z_lineReducing the need for appropriate design guidelines for the sense winding.

Z_lineAt the first self-resonant frequency f of the CM choke_r，cm(given as

) And then is determined mainly by parasitic capacitance. Thus, the frequency f_r，cmSubsequent inductive cancellation terms X(s) vs Z_lineHas no significant effect on the size of (c). Furthermore, only when sN_sen ²L_cmHigher than (Z)_in,AEF||Z_sen,para) X(s) in equation 3 is significant. Thus, if sN_sen ²L_cmInitially becomes greater than (Z)_in,AEF||Z_sen,para) Is higher than f_r，cmThen Z is_lineHardly affected by the sensing winding. These conditions can be satisfied by the following design procedure. First, in all frequency ranges of interest (e.g., 10kHz to 30MHz), Z_in，AEFIs designed to be higher than Z_sen，para. That is, it can be expressed as the condition of equation 14.

[ formula 14]

More simply, R_fAnd C_fAs shown in equations 15 and 16.

[ formula 15]

[ formula 16]

C_f＜C_ser

If the inequality condition in equation 14 is sufficiently satisfied, then it is (Z)_in,AEF||Z_sen,para)≈Z_sen,para. Then, sN_sen ²L_cmInitially becomes greater than (Z)_in,AEF||Z_sen,para) Is approximately equal to N_sen ²L_cmAnd C_senAs shown in equation 17.

[ formula 17]

Then, due to f_r，senMust be higher than f_r，cmThe values of the coefficients, as in equation 18,

design guidelines for the number of turns of the sense winding are derived, as shown in accordance with equation 19.

[ formula 19]

Here, L_cm,effIs approximately (1+ k)_cm)L_cm≈2L_cm. Can guarantee to maintain Z_lineThe design guideline of equation 19 of (a) is derived by sensing the maximum allowable winding of the winding. CM choke and C in equation 19_cm,C_senThe exact value of parasitic capacitance of (a) is actually unknown prior to design, but equation 19 may still provide a useful guide for the number of turns of the sense winding.

FIG. 7 shows the power line impedance (Z) from the Y capacitor position toward the power supply_line) Curve (c) of (d). (a) Is shown when N_senIn case of violating equation 19, (b) represents N_senThe case when equation 19 is satisfied. Examples of the numerical values are shown in FIG. 7. By mixing C_cmAnd C_senDesign AEF to the same fixed value, which is used to design two different N_senValues were analyzed briefly. Each Z was compared between the case without AEF and the case with AEF_lineBy comparison of Z_{line w/o,AEF}And Z_{line w/,AEF}. In FIG. 7(a), N _sen2 violates conditional formula 19, and f_r，senLower than f_r，cm. In contrast, in fig. 7(b), N sen ═ 0.5 satisfies formula 19, and f_r，senHigher than f_r，cm. As a result, in FIG. 7(a), Z_{line,w/o AEF}Compared with, Z_{line w/,AEF}Significantly reduced, whereas in FIG. 7(b), Z_{line w/,AEF}Hardly changed.

In addition, when AEF is used, Z is in the high frequency region_lineAnother resonance occurs. As shown in fig. 7(a) and (b), through the sensing winding

Produces resonance at the frequency of (c). Due to this resonance, the resonance will be tuned to the system in the high frequency rangeThe stability of the feedback is adversely affected, and therefore the input terminal of the operational amplifier needs to be controlled by R_fAnd C_fA low pass filter is formed to suppress resonance. For a low pass filter that does not affect the AEF performance over the operating frequency range, the cut-off frequency of the filter should be greater than the maximum operating frequency f_op，maxBut should be less than the resonant frequency of equation 20.

[ formula 20]

Equation 15, equation 16, and equation 20 may become design guidelines for the low pass filter.

Next, the design of the injection transformer and the amplification unit will be described.

The design of the injection transformer and amplification unit assembly mainly determines the main performance parameter f of the AEF of fig. 6_op，min，f_op，maxAnd C_y，eff. Capacitor C at output end of amplifying unit_oFor blocking unwanted signals having frequencies below the target operating frequency range. And L_injC in series_oA high frequency filter is constructed whose cutoff frequency is derived as shown in equation 21 to determine the minimum operating frequency of the AEF.

At f_op,minAt a frequency of, and L_injC connected in series_oRapidly decreases, thereby increasing the output current of the operational amplifier. Thus, although R_oIs added to the operational amplifier output to limit the impedance at the resonant frequency, but must be sufficiently less than sL over all operating frequency ranges_inj。

At the same time, as described in FIG. 6a, the maximum operating frequency f of the AEF_op，maxDetermined by the frequency boundary where the impedance of the bypass branch is lower than the impedance of the injection transformer path. Similar to the resonance induced by the induction winding shown in FIG. 7, injectionThe resonance in the secondary winding of the transformer causes feedback instability and therefore the bypass branch must start operating at a frequency below the resonance frequency. The resonance of the secondary winding occurs above f as shown in equation 22_op，maxFrequency of (2)

The above.

[ formula 22]

According to the inductive part (1-k) of the injection transformer_inj ²)N_inj ²L_injAnd bypass branch circuit capacitor C_dTo determine f_op,maxAs in equation 23.

[ formula 23]

Substituting equation 23 into equation 22 yields C_dAnd C_inj ²The relationship between them is as follows.

[ formula 24]

C_d＞C_inj ²

In order to remain stable at high frequencies, some damping resistor R is required_d1And R_d2. It is recommended to use R of several tens of ohms (ohm)_d2To mitigate the resonance of the Y capacitance and CM noise source impedance in the high frequency range, as will be shown experimentally in chapter IV.

It is assumed that the resistance R in AEF operation except the resonance point can be neglected_d1And R_d2And R_inj ²The conditions of equation 24, equation 7 through equation 11 may be set at f_op，maxIs estimated according to equation 25.

[ formula 25]

α(s)≈N_senN_injG_amp(s)，β(s)≈0

Y capacitance, effective capacitance C in equation 12_Y，eff(s) is simplified by equation 26.

[ formula 26]

C_Y，eff(s)≈(1+N_senN_injG_amp(s))C_Y

G_ampPhase compensation element R of(s)_cAnd C_cAEF operation should be hardly affected and equation 26 is further reduced to a frequency independent value as shown in fig. 6.

[ formula 27]

C_Y，eff≈(1+N_senN_inj(1+R₂/R₁))C_Y

Finally, several useful design guidelines for AEF can be derived as follows. Although N is_senLimited by equation 19, but in equation 27, N may be increased by_injAnd gain of the amplifying unit (1+ R)₂/R₁) Mixing C with_Y，effIs designed as C_YSeveral times higher than that of the prior art. However, with N_injIncrease of (2), maximum operating frequency f_op，maxWill be reduced according to equation 23. In addition, high amplifier gain requires that the operational amplifier have a large output voltage swing and a large gain bandwidth. Therefore, the cost of the operational amplifier and the f of the AEF should be considered_op，maxSelecting an appropriate N_injAnd (1+ R)₂/R₁) The value is obtained.

Furthermore, the condition of equation 22 means that N can pass through the injection transformer_inj，L_injAnd C_inj ²To adjust f of AEF_op，max. Due to parasitic capacitance C_inj ²Is not an independent design parameter, so N should be_injAnd L_injDesigned smaller to achieve higher f_op，max. However, smaller N_injMake C_y，effDecrease of L_injDecrease, then f in equation 21_op，minIt will increase. Therefore, we propose the following design process to optimize the AEF performance. First, in a physical package of a given size, C is put in_oDesigned to be as large as possible and for the purposeMark f_op，minMixing L with_injDown to the limit of equation 21. Next, for goal f_op，ma'xWill N_injIncrease to the limit of equation 22 to obtain the maximum C_Y，eff。

Next, the stability check will be described.

The AEF is essentially a feedback system with an analog input and an analog output, which must be carefully designed and guaranteed for stability. If the system is unstable, the system will oscillate even if the EUT noise source is not applied. Feedback stability can be verified by the phase of the loop gain and the gain margin. To derive the loop gain from the circuit model of fig. 4, the feedback loop is separated from the output of the operational amplifier, and a test voltage source V from the separation node is used_tApplied to an injection transformer and without applying a noise source voltage V_nVoltage V of the front-end node of the CM choke_inAnd a test voltage V_tThe ratio of (d) can be calculated according to equation 28.

[ formula 28]

Wherein,

[ formula 29]

(V_in,amp/V_in) And (V)_out,amp/V_in,amp) Is derived as G in equations 9 and 10, respectively₁(s) and G_amp(s). Therefore, the loop gain of the system can be expressed as equation 30.

[ formula 30]

Using R_cAnd C_cWith the object of providing the effective inductance L of the choke_cm,effAnd the effective capacitance C of the Y capacitance branch_Y,effThere is a risk of instability due to resonance between, and thus G is increased for stability in the low frequency range_loopPhase margin of(s). Resonant frequency

The low frequency boundary at which the filter operates is determined and should be below the low frequency limit of the CE standard in proper EMI filter design. As shown in equation 31, the calculation is due to R_cAnd C_cThe maximum amount of phase compensation incurred.

[ formula 31]

Equation 31 at frequency

The following occurs.

∠C_{loop，w/comp}(S) denotes G with phase compensator_loopPhase of(s), and < G_{loop，w/ocomp}(S) denotes G without a phase compensator_loopThe phase of(s). By setting the maximum phase compensation frequency to

Can derive R from the resonance frequency of_cAnd C_cSuch as equation 32.

[ formula 32]

Expression of equations 31 and 32 as R_cAnd C_cDesign guidelines are provided.

Due to G in equation 28₂(s) impedance Z of the noise source according to EUT_nAre varied and should therefore be notedThe loop gain in equation 30 is also the same. In equation 30, it can be seen that with Z_nThe loop gain increases and thus the gain margin tends to decrease. Thus, with Z_nDesigning stability for infinity (infinite) will generally provide stability under worst case conditions. Therefore, in this specification, Z at an infinite value_nThe loop gain of the designed AEF is calculated or measured under conditions to ensure stability in any EUT application.

FIG. 8 is a comparison of the loop gain, where (a) shows the gain in the absence of the damping component R_d1，C_dAnd R_d2And a phase compensator R_c，C_cThe loop gain in the unstable case of (a), (b) shows the loop gain in the stable case where these components exist.

For example, G of a filter with AEF can be expressed using equation 30_loo_p(s) as shown in FIG. 8. Bypass branch and phase compensator R_d1、C_d、R_d2、R_c、C_cNot installed in fig. 8(a), but installed in fig. 8 (b). Their effect on stability has been clearly shown. In fig. 8(a), the instability due to the sudden phase shift around 10MHz is due to the secondary winding of the injection transformer and is resolved by the bypass branch in the case of fig. 8 (b). In FIG. 8(a), at low frequencies less than 100kHz, L_cm,effAnd C_Y,effThe resonance between them may cause excessive phase shifts and risks of instability. As can be seen from FIG. 8(b), a phase compensator R is used_cAnd C_cThe gain margin is greatly increased.

Next, selection and overall design steps of the operational amplifier will be described. Operational high frequency limit f of operational amplifier in non-inverting amplifier_OPampMust be above the high frequency limit f of the CE standard_CE,max。

[ formula 33]

f_OPamp＞f_CE，max

In addition, the voltage and current capacity of the operational amplifier must be sufficient to compensate for noise. For calculating the required operational amplifier capacity, respectivelyEquations 34 and 35, the voltage V at the output of the operational amplifier is calculated according to the circuit model of FIG. 4_out,amp(s), current I_out,amp(s)。

[ formula 34]

V_out，amp(s)＝V_in(s)G₁(s)G_amp(s)

[ formula 35]

Wherein,

[ formula 36]

Due to V_in(s) is determined not only by the filter impedance, including the AEF, but also by Z_nAnd V_n(s) determination, therefore noise source model information is needed for estimating V_out,amp(s) and I_out,amp(s). The SMPS, Z, in operation can be derived by various measurement methods that have been developed_nAnd V_n(s) noise source model. Derivation of Z_nAnd V_nAfter(s), the operational amplifier outputs a voltage v_out,amp(t) and output current i_out,ampThe time domain waveform of (t) may be represented by V given in equations 34 to 36_out,amp(s) and I_out,amp.The spectrum of (2) was calculated. Thus, the voltage capacity v of the operational amplifier output_OPamp,maxAnd current capacity i_OPamp,maxShould be sufficient to provide the calculated v separately_out,amp(t) and i_out,amp(t)。

[ equation 37]

v_OPamp，max＞max(|v_out，amp(t)|)

[ formula 38]

i_OPamp，max＞max(|2i_out，amp(t)|)

Since I is defined in half-circuit (half-circuit) model_out,amp(s) thus flow through the operationThe actual current of the amplifier is twice the calculated current as shown in equation 38.

As shown in equation 35, under influence I_out,amp(s) among various design factors, N is increased_injWill greatly increase the I in the operating frequency range of the AEF_out,amp(s). From N_injThe resulting voltage gain of the injection transformer, as opposed to increasing the output current as described above, may lower the output voltage of the operational amplifier. The injection transformer not only isolates the AEF ground from the SMPS ground, but also provides additional design flexibility for the gain and op amp circuits.

Other embodiments of the isolated active EMI filter without additional components on the power line according to the present invention will be described, and fig. 9 is a circuit diagram of embodiment 2 of the isolated active EMI filter without additional components on the power line according to the present invention. A 2 nd embodiment of an isolated active EMI filter without additional elements on the power line according to the present invention includes a Common Mode (CM) choke 1710, a Y capacitor 1720, a transforming unit 1730, an amplifying unit 1740, and a compensation winding 1750.

Referring to fig. 9, a Common Mode (CM) choke 1710 is disposed at a power supply side, and a Live line (Live line) and a Neutral line (Neutral line) connected to an EMI source are respectively wound with windings.

Y capacitor 1720 is configured on the side of the EMI source that generates EMI and consists of two capacitors connected in series, in parallel between the hot and neutral conductors, and in common with ground.

A transforming unit 1730 is installed at the front end of the Y capacitor 1720, and a primary coil senses a noise voltage of the Y capacitor, transforms it, and is isolated from a power line (isolated).

The amplifying unit 1740 amplifies the noise voltage sensed and transformed by the transforming unit 1730.

The compensation winding 1750 is rewound on the common mode choke 1710 through a coil, and injects the noise signal amplified by the amplifying unit into the common mode choke 1710.

Fig. 10 is a circuit diagram of a 3 rd embodiment of an isolated active EMI filter without additional elements on a power line according to the present invention, including a Common Mode (CM) choke 1810, a Y capacitor 1820, a sensing winding 1830, an amplifying unit 1840, and a transforming unit 1850.

Referring to fig. 10, the common mode choke 1810 is disposed at one side of an EMI source generating EMI, and a Live line (L) and a Neutral line (N) connected to the EMI source are respectively wound with windings.

The Y capacitor 1820 is disposed on the power supply side, and is composed of two capacitors connected in series, which are connected in parallel between the live line (L) and the neutral line (N), and are connected in common to ground.

The sensing winding 1830 is rewound on the common mode choke 1810 by a coil, and senses a noise current of the common mode choke 1810.

The amplification unit 1840 amplifies the noise current sensed by the sensing winding 1830.

The transforming unit 1850 is disposed at the front end of the Y capacitor 1820, the primary coil receives the amplified signal from the amplifying unit 1840, and the secondary coil is connected to the ground connected to the Y capacitor 1820 to be isolated (isolated) from a power line, and injects the signal transformed by the secondary coil as a compensation signal to the Y capacitor 1820.

Fig. 11 is a circuit diagram of a 4 th embodiment of an isolated active EMI filter without additional elements on a power line according to the present invention, which includes a Common Mode (CM) choke 1910, a Y capacitor 1920, a transforming unit 1930, an amplifying unit 1940, and a compensation winding 1950.

Referring to fig. 11, a common mode choke coil 1910 is disposed at one side of an EMI source generating EMI, and a Live line (Live line) and a Neutral line (Neutral line) connected to the EMI source are wound with windings, respectively.

The Y capacitor 1920 is configured on the power supply side of the power supply and is composed of two capacitors connected in series, the two capacitors being connected in parallel between the line and neutral conductors and being connected in common to ground.

A transformer 1930 is provided at the front end of the Y capacitor 1920, and a primary coil senses the noise voltage from the Y capacitor 1920 and transforms it through a secondary coil, and is isolated from a power supply line (isolated).

The amplification unit 1940 amplifies the noise voltage transformed by the transformer 1930.

The compensation winding 1950 is rewound on the common mode choke 1910 by a coil, and injects a noise signal amplified by the amplifying unit 1940 as a compensation signal into the common mode choke 1910.

Referring to fig. 1 and 12, first, a passive EMI filter in which a common mode choke coil 110 is disposed on a power supply side and a Y capacitor 120 is disposed on an EMI source side is prepared (step S2010), that is, the Common Mode (CM) choke coil 110 is disposed on a power supply side of power supply, and a Live line (Live line) and a Neutral line (Neutral line) connected to the EMI source are wound with windings, respectively. The Y capacitor 120 is disposed at one side of the EMI source generating EMI, and is composed of two capacitors connected in series, which are connected in parallel between the line (L) and neutral (N) and are commonly connected to ground.

The EMI noise current of the common mode choke coil 110 is sensed by the sensing winding 130 formed by rewinding the common mode choke coil 110 with a coil (step S2020), and the amplifying unit 140 amplifies the noise current sensed by the sensing winding 130 (step S2030).

The signal amplified by the amplifying unit 140 is received through the primary coil of the transformer 150 installed at the front end of the Y capacitor 120 (step S2040), and then transformed through the secondary coil of the transformer 150 and injected into the Y capacitor 120 (step S2050). Here, the secondary coil of the transformer 150 is connected to the ground connected to the Y capacitor 120 and isolated (isolated) from the power supply line.

Fig. 13 shows a flowchart of a method for reducing EMI noise by adding an active component in a passive EMI filter, which corresponds to embodiment 2 of the isolated active EMI filter without an additional component on the power line according to the present invention. Referring to fig. 9 and 13, first, a passive EMI filter in which the common mode choke 1710 is provided on the power supply side and the Y capacitor 1720 is provided on the EMI source side is prepared (step S2110). More specifically, the common mode choke 1710 is disposed on the power supply side of the power supply, and a Live line (Live line) and a Neutral line (Neutral line) connected to the EMI source are wound with windings, respectively. Y capacitor 1720 is disposed on the side of the EMI source that generates EMI, and is composed of two capacitors connected in series, which are connected in parallel between the hot line (L) and neutral line (N), and are commonly connected to ground.

The primary coil of the transformer 1730 mounted at the front end of the Y capacitor 1720 senses a noise voltage using the Y capacitor 1720 as a sensing capacitor (step S2120)). The sensed noise voltage is transformed using the secondary coil of the transformer 1730 (S2130 step). Here, the secondary winding of the transformer 1730 is connected to ground connected to the Y capacitor 1720, thereby being isolated (isolated) from the power supply line.

The amplifying unit 1740 amplifies the voltage transformed from the secondary coil of the transformer 1730 (step S2140). The amplified noise signal is injected into the common mode choke coil by the compensation winding 1750 formed by rewinding the common mode choke coil with a coil (step S2150).

Referring to fig. 10 and 14, first, a passive EMI filter in which the common mode choke 1810 is provided on the EMI source side and the Y capacitor 1820 is provided on the power source side is prepared (step S2210). Specifically, a Common Mode (CM) choke 1810 is disposed at one side of an EMI source generating EMI, and a Live line (L) and a Neutral line (N) connected to the EMI source are respectively wound with windings. The Y capacitor 1820 is disposed on the power supply side, and is composed of two capacitors connected in series, which are connected in parallel between the line (L) and neutral (N) and are connected in common to ground.

The noise current of the common mode choke 1810 is sensed by the sensing winding 1830 formed by rewinding the common mode choke 1810 with a coil (step S2220), and the amplifying unit 1840 amplifies the noise current sensed from the sensing winding 1830 (step S2230).

The signal amplified by the amplifying unit 1840 is input to a primary coil of the transformer 1850 installed at the front end of the Y capacitor 1820 (step S2240), and then the signal input to the primary coil is transformed by a secondary coil of the transformer 1850 and injected into the Y capacitor 1820 as a compensation signal (step S2250). Here, the secondary winding of the transformer 1850 is connected to ground connected to the Y capacitor 1820, thereby being isolated (isolated) from the power supply line.

Fig. 15 shows a flowchart of a method for reducing EMI noise by adding an active component in a passive EMI filter, which corresponds to embodiment 4 of the isolated active EMI filter without an additional component on the power line according to the present invention. Referring to fig. 11 and 15, a passive EMI filter in which the common mode choke 1910 is provided on the EMI source side and the Y capacitor 1920 is provided on the power supply side is prepared (step S2310)

More specifically, the common mode choke coil 1910 is disposed at one side of an EMI source generating EMI, and a Live line (L) and a Neutral line (N) connected to the EMI source are respectively wound with windings. The Y capacitor (1920) is arranged on the power supply side of the power supply and consists of two capacitors connected in series, wherein the two capacitors are connected in parallel between the live line (L) and the neutral line (N) and are commonly connected with the ground.

The primary coil of the transformer 1930 installed at the front end of the Y capacitor 1920 senses the noise voltage of the Y capacitor 1920 (step S2320). The noise voltage sensed by the primary coil is transformed by the secondary coil of transformer 1930 (step 2330), where the secondary coil of transformer 1930 is connected to ground connected to Y-capacitor 1920, thereby being isolated from the power supply line.

The amplifying unit 1940 amplifies the noise voltage transformed from the secondary coil (step 2340). The compensation winding 1950 injects the amplified noise signal as a compensation signal into the common mode choke 1910, and the compensation winding is formed by rewinding the common mode choke 1910 with a coil (step 2350).

In the above, the isolated type active EMI filter without additional components on the power line according to the present invention is an active filter of a form additionally mounted on the existing passive EMI filter composed of the common mode choke coil and the Y capacitor. The present invention proposes a choke element which is added to a power supply line by rewinding a noise sensing or compensation line on a common mode choke present in a passive EMI filter. The Y-capacitance present in the passive EMI filter serves as a compensation or sensing capacitor and a small transformer is installed in front of the compensation or sensing capacitor to isolate the active circuit from the power supply line, with the advantage that no additional components are required to be added to the power supply line and to isolate the active circuit from the power supply line.

The isolated active EMI filter according to the present invention wraps the sensing and compensation lines around with an optimal number of turns (turn) so as not to degrade the noise attenuation performance of the passive EMI filter itself. The transformer turn (turn) ratio (ratio) is adjusted to optimize noise sensing and compensation performance through the Y-capacitor and the small transformer of the front end, and to optimize the gain of the active filter amplification unit. Various stability compensation circuits may be added to ensure feedback stability of the entire feedback circuit structure for noise sensing and compensation. The active EMI filter of the present invention is a feedback circuit structure for sensing noise and injecting a compensation signal.

According to an embodiment of the present invention, the low-band conducted noise is reduced by 11dB when only the passive filter is used, but is reduced by 26dB when the Active EMI Filter (AEF) of the present invention is additionally installed. In the case of using only the passive filter, an expensive common mode choke coil must be used, or the total number of stages of the filter must be increased to sufficiently attenuate noise in a low frequency band.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and it will be understood by those of ordinary skill in the art that various modifications and other equivalent embodiments may be made thereto. Therefore, the true technical scope of the present invention should be determined by the technical idea of the appended registration claims.

Claims

1. An isolated active EMI filter without additional components on a power line, comprising:

a Common Mode (CM) choke coil disposed on a power supply side of a power supply and having a winding wound around a line conductor and a neutral conductor connected to an EMI source, respectively;

a Y capacitor, which is disposed at one side of an EMI source generating EMI, and is composed of two capacitors connected in series, the two capacitors being connected in parallel between the line and neutral lines and connected in common with a ground;

a sensing winding which is rewound on the common mode choke coil through a coil and senses a noise current of the common mode choke coil;

an amplifying unit that amplifies a noise current sensed by the sensing winding; and

and a transformer disposed at a front end of the Y capacitor, a primary coil receiving the amplified signal from the amplifying unit, a secondary coil connected to a ground connected to the Y capacitor so as to be isolated from a power line, and injecting a signal of the secondary coil as a compensation signal into the Y capacitor.

2. The isolated active EMI filter without additional components on a power line of claim 1,

further comprising a bypass branch comprising

A 1 st resistor (R) having one end connected to the Y capacitor and the other end connected to the secondary coil of the transformer_d1)；

A capacitor (C) having one end connected to a segment of the resistor_d)；

A 2 nd resistor (R) having one end connected in series with the other end of the capacitor and the other end connected to ground_d2)，

And stabilizing bypass and damping circuitry to avoid resonance in the transformer and mitigate performance degradation due to resonance between the EMI source impedance and the Y capacitance.

3. The isolated active EMI filter without additional components on a power line of claim 1,

when the capacitance of the parasitic circuit of the Common Mode (CM) choke is Ccm and the capacitance of the parasitic circuit of the sensing winding is Csen, the number of turns of the sensing winding (Nsen) is less than the square root of 2 Ccm/Csen.

4. An isolated active EMI filter without additional components on a power line, comprising:

the voltage transformation unit is arranged at the front end of the Y capacitor, a primary coil senses the noise voltage of the Y capacitor, and a secondary coil transforms the noise voltage and is isolated from a power line;

an amplifying unit that amplifies the noise voltage sensed by the transforming unit and transformed;

a compensation winding that is rewound on the common mode choke coil through a coil and injects the noise signal amplified by the amplification unit into the common mode choke coil.

5. An isolated active EMI filter without additional components on a power line, comprising:

a Common Mode (CM) choke coil disposed on an EMI source side that generates EMI, and having a winding wound around a line conductor and a neutral conductor connected to the EMI source, respectively;

a Y capacitor, which is configured on the power supply side of the power supply and consists of two capacitors connected in series, wherein the two capacitors are connected in parallel between the live line and the neutral line and are commonly connected with the ground;

and a transformer disposed at a front end of the Y capacitor, a primary coil receiving the amplified signal from the amplifying unit, a secondary coil connected to a ground connected to the Y capacitor so as to be isolated from a power line, and injecting a signal transformed by the secondary coil as a compensation signal into the Y capacitor.

6. An isolated active EMI filter without additional components on a power line, comprising:

a Common Mode (CM) choke coil disposed at one side of an EMI source generating EMI, and having windings wound around a live line and a neutral line connected to the EMI source, respectively;

a transformer disposed at a front end of the Y capacitor, a primary coil sensing a noise voltage from the Y capacitor and transforming the same through a secondary coil, and being isolated from a power line;

an amplifying unit that amplifies the noise voltage transformed by the transformer; and

a compensation winding that is rewound on the common mode choke coil through a coil and injects the noise signal amplified by the amplifying unit into the common mode choke coil as a compensation signal.